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spdee31 said:
i got a 350 block 30over flat top pistons w 6"rods. question is what should i go with 350 or 400 crank? going in 4x4 jeep thanks
The real question is....what is the compression height of the pistons?

The nominal block deck height of a 350 block is 9.025". The stock "stack" of parts used in that block is 9.000" (1.740" crank radius, 5.700" rod and 1.560" piston compression height), leaving a piston deck height of 0.025".

No matter the combination of parts you use, the stack needs to add up to somewhere around 9.000", give or take a little depending on block deck height and where you want the piston deck height to end up.

If you have a 350 crank with 6.000" rods, then the piston compression height needs to be somewhere around 1.260". If you use a 400 crank with the main bearing journals turned down to 2.450" so it will drop into the 350 main saddles, or an aftermarket crank with a 3.750" stroke (383 crank), then the piston compression height needs to be on the order of 1.125", so you need to know the compression height of the pistons you have before you go any farther.

If the pistons are stamped with a part number, research the number and find the compression height. If you can't find a number, use a 6" dial caliper. Hook one jaw into the top of the wrist pin bore and the other jaw onto the crown of the piston. Write down the dimension. Add .464 to that dimension (radius of the wrist pin bore). If you get a dimension of somewhere around 1.260 (within a couple of thousandths), then the pistons were made to be used with a 350 crank. If you get a dimension of 1.125, then the pistons were meant to be used with the 3.750" stroke of a 400 crank or aftermarket 3.750" stroke crank (383).
 
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